Apparatus and method for slurry distribution

ABSTRACT

A assembly for a chemical mechanical polishing apparatus includes a carrier head and a polishing liquid delivery ring. The carrier head has a substrate receiving surface and a retaining ring surrounding the substrate receiving surface. The polishing liquid delivery ring is coupled to the carrier head and surrounds the retaining ring. The polishing liquid delivery ring includes a reservoir to hold a liquid and an outlet in fluid communication with the reservoir and positioned to dispense the liquid to a location on a polishing surface outside the retaining ring.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application SerialNo. 60/822,920, filed on Aug. 18, 2006, which is incorporated herein byreference.

BACKGROUND

The present invention relates generally to distribution of a polishingliquid during chemical mechanical polishing.

Integrated circuits are typically formed on substrates, particularlysilicon wafers, by the sequential deposition of conductive,semiconductive or insulative layers. After each layer is deposited, itis etched to create circuitry features. As a series of layers aresequentially deposited and etched, the outer or uppermost surface of thesubstrate, i.e., the exposed surface of the substrate, becomesincreasingly nonplanar. This nonplanar surface presents problems in thephotolithographic steps of the integrated circuit fabrication process.Therefore, there is a need to periodically planarize the substratesurface.

Chemical mechanical polishing (CMP) is one accepted method ofplanarization. This planarization method typically requires that thesubstrate be mounted on a carrier or polishing head, and pressed againsta polishing surface, such as a rotating pad or linear belt. A polishingliquid, such as a slurry with abrasive particles, can be introduced ontothe polishing pad to assist the polishing process.

SUMMARY

In one aspect, the invention is directed to an assembly for a chemicalmechanical polishing apparatus that includes a carrier head and apolishing liquid delivery ring. The carrier head has a substratereceiving surface and a retaining ring surrounding the substratereceiving surface. The polishing liquid delivery ring is coupled to thecarrier head and surrounds the retaining ring. The polishing liquiddelivery ring includes a reservoir to hold a liquid and an outlet influid communication with the reservoir and positioned to dispense theliquid to a location on a polishing surface outside the retaining ring.

In another aspect, the invention is directed to a method for deliveringa polishing liquid. The method includes delivering a polishing liquidinto a reservoir of a polishing liquid delivery ring coupled to acarrier head, and dispensing the polishing liquid from the reservoirthrough an outlet in fluid communication with the reservoir to alocation on a polishing surface outside a retaining ring of the carrierhead.

Implementations of either invention may include one or more of thefollowing features. The reservoir may be a recess, e.g., an annularrecess surrounding the carrier head, formed in an upper surface of thepolishing liquid delivery ring. A passage may be formed through thepolishing liquid delivery ring from the reservoir to the outlet. Thepassage may be essentially vertical or tilted, e.g., angled outwardlyfrom top to bottom. The outlet may be located on a bottom surface of theretaining ring. The polishing liquid delivery ring may include aplurality of outlets in fluid communication with the reservoir, eachoutlet positioned to dispense the liquid to an associated location onthe polishing surface outside the retaining ring. The retaining ring mayhave a bottom surface with slurry delivery channels. The polishingliquid delivery ring may include an inwardly extending flange positionedon a top surface of the carrier head. The flange may be positioned on atop surface of the retaining ring, e.g., between the top surface of theretaining ring and a bottom surface of a housing of the carrier head. Tepolishing liquid delivery ring may be coupled to the carrier head by abearing. A supply tube may have an outlet positioned at leastintermittently over the polishing liquid delivery ring. A carrier headsupport may hold the carrier head, and a pump may be supported on thecarrier head support to pump polishing liquid through the supply tube. Apolishing liquid supply fluidly may be coupled to the pump and securedto the carrier head support. The pump is configured to dispense thepolishing slurry into the reservoir intermittently or continuouslyduring polishing.

The invention may provide one or more of the following advantages. Theslurry distribution system can provide slurry to an area immediatelyadjacent the substrate. This can ensure more uniform slurry distributionnear the substrate edge, thus improving within-wafer nonuniformity anddecreasing edge exclusion. In addition, slurry consumption can bereduced, thus reducing both consumable costs and the occurrence of driedslurry, thereby reducing defects.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of a chemical mechanical polishing apparatus.

FIG. 2 is a cross-sectional view of an exemplary carrier head having anexternal feed line and slurry delivery ring.

FIG. 3 is an expanded view of the slurry delivery ring.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

As shown in FIG. 1, a substrate 10 is polished at a polishing station 25of a chemical mechanical polishing (CMP) apparatus 20. A description ofa suitable CMP apparatus may be found in U.S. Pat. No. 5,738,574, theentire disclosure of which is incorporated herein by reference. Thistype of CMP apparatus includes a machine base 22 that supports threepolishing stations 25 and a transfer station 27. Each polishing stationincludes a rotatable platen 30 on which is placed a polishing pad 32.Each polishing station 25 may further include a pad conditioner tomaintain the abrasive condition of the polishing pad 32.

As shown in FIGS. 1 and 2, this implementation of the CMP apparatus 20also includes a cross-shaped rotatable multi-head carousel 40 thatsupports four carrier heads 50. The carousel 40 can rotate to orbit thecarrier heads 50, and the substrates 10 attached thereto, between thepolishing stations 25 and the transfer station 27. Each carrier head 50can independently rotate about its own axis, and can laterally oscillatein a radial slot 42 formed in a carousel support plate 44. A drive shaft46 extends through the slot 42 connecting a motor 48 to the carrier head50. The motor 48 and drive shaft 46 can be supported on a slider (notshown) that is linearly driven along the slot 42 by a radial drive motor(not shown) to laterally oscillate the carrier head 50.

As shown in FIG. 2, the carrier head 50 can include a housing or base 52and a flexible membrane 54 clamped to the housing 52 to form a loadingchamber 56. The housing 52 is connected to the drive shaft 46, and maybe generally circular in shape to correspond to the circularconfiguration of the substrate 10. Fluid can be injected into theloading chamber 56 through a passage in the housing 52 and the driveshaft 46 to pressurize the loading chamber 56 and apply a load (i.e., adownward pressure) to the substrate. The carrier head 50 can includeother elements that are not shown, for example, more complicatedpneumatics, e.g., a chamber to control pressure on the retaining ring ormultiple chambers to apply independently controllable pressures ondifferent portions of the substrate. A discussion of a similar carrierhead is found in U.S. Patent Publication No. 2006-0154580, the entiredisclosure of which is incorporated herein by reference.

The carrier head 50 also includes a retaining ring 60 secured to thebottom of the housing 52, e.g., by bolts (not shown). The retaining ring60 has an inner surface 62 to engage the substrate 10 and prevent thesubstrate from slipping or sliding from beneath the carrier head 50during polishing, and a bottom surface 64 which can contact and compressthe polishing pad. The bottom surface 64 can be substantially flat, oroptionally, slurry distribution channels can be formed in the bottomsurface 64 of the retaining ring 60.

Referring to FIGS. 2 and 3, the slurry delivery ring 100 is attached tothe outer circumference of the carrier head 50. The slurry delivery ring100 can be a generally annular body with a recess 102 formed in its topsurface 104 to provide a reservoir for a polishing liquid, such asslurry 34. The recess 102 can be an annular depression extendingentirely around the carrier head. The recess can have a generallysemi-circular cross section. Alternatively, the recess can have be aparallelepiped, and can have inner and outer walls that are slantedoutwardly from top to bottom. The depth of the recess 102 determines theavailable volume for the slurry reservoir.

The slurry delivery ring 100 can include an inwardly projecting flange120 that, when the slurry delivery ring 100 is lowered onto the carrierhead 50, rests on a horizontal surface of the retaining ring 60 or thehousing 52 to hold the slurry delivery ring 100 in place. Alternatively,the flange 120 can be clamped between a top surface of the retainingring 60 and a bottom surface of the housing 52. In either case, in thisposition, a bottom surface 106 of the slurry delivery ring 100 is spacedaway and does not contact the polishing pad 32. The slurry delivery ring100 can be constructed of a plastic such as polyphenyl sulfide (PPS) ora metal such as stainless steel, and the passages 110 can be formed byprecision machining.

A plurality of passages 110, e.g., three to twelve passages, such asfour or eight passages, are formed through the slurry delivery ring 100to fluidly couple the recess 102 to corresponding outlets 112 on thebottom surface 106 of the slurry delivery ring 110. Specifically,gravity causes the slurry 35 in the recess 102 to drain through thepassages 110 and out of the outlets 112 and onto the surface of thepolishing pad 32. In particular, the outlets 112 are positioned todispense the liquid to a location on a polishing surface that is nearyet outside the outer diameter 64 of the retaining ring 60.

The passages can be distributed at equal angular intervals around theslurry delivery ring. In one implementation, the passages 110 areessentially vertical. Alternatively, the passages can be tilted. Thediameter and angle of the passages 110 determines the speed at which thereservoir will drain. If the passages are angled inwardly from top tobottom, centrifugal forces will tend to prevent the slurry from flowingthrough the passage, thereby decreasing the slurry delivery rate. On theother hand, if the passages are angled outwardly from top to bottom,centrifugal forces will tend to aid flow the slurry through the passage,thereby increasing the slurry delivery rate. Increasing the passagediameter will increase the slurry flow rate, whereas decreasing thepassage diameter will reduce the slurry flow rate.

The recess 102 is open to the atmosphere, and can be fed slurry 35 by anexternal feed tube 70. In one implementation, the feed tube 70 isextends below the underside of the carousel 40 and has an outlet 72positioned over the recess 102. The slurry 35 can be metered through thefeed tube 70 by a metering pump (not shown) that is located in thecarousel 40. A slurry supply from which the slurry is pumped can belocated in the carousel 40, or in the machine base, or outside thepolishing apparatus 20. The slurry can be dispensed at a rate sufficientto replace slurry that is consumed during polishing. If the feed tube 70is attached to the slider and oscillates laterally with the carrierhead, then slurry can be dispensed into the into the delivery ringeither on a continuous basis or intermittently. Alternatively, if thefeed tube 70 is attached to carousel but does not oscillate laterallywith the carrier head, then the slurry can be dispensed intermittently,e.g., each time that the sweep of the carrier head carries the slurrydelivery ring 100 beneath the outlet of the feed tube 70. If the slurryis dispensed intermittently, sufficiently slurry may be dispensed intothe reservoir to polish a set number of substrates, e.g., one substrate.When the set number of substrate has been polished, the carrier head 50is moved into position with the slurry delivery ring 100 carrier and theslurry reservoir is refilled.

In the implementation described above, the slurry delivery ring 100rotates with the carrier head 50. However, the slurry delivery ring 100could be mounted on carrier head 50 with a clutch or bearing assembly sothat the delivery ring sweeps but does not necessarily rotate with thecarrier head.

By providing slurry to an area proximate to the interface between thesubstrate and a rotating polishing pad, the invention can improve andenhance the uniformity of planarization of the substrate, reduce edgeexclusion, and reduce the amount of slurry applied to the pad.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the slurry delivery ring could be used with otherconfigurations of carrier head, such as a carrier with a rigid backingmember, with other polishing articles, such as linear polishing belts,and other polishing system architectures, such as polishing systems withdifferent number or configuration of polishing stations or polishingsystems that do not use a carousel at all. Accordingly, otherembodiments are within the scope of the following claims.

1. An assembly for a chemical mechanical polishing apparatus,comprising: a carrier head with a substrate receiving surface and aretaining ring surrounding the substrate receiving surface; and apolishing liquid delivery ring coupled to the carrier head andsurrounding the retaining ring, the polishing liquid delivery ringincluding a reservoir to hold a liquid and an outlet in fluidcommunication with the reservoir and positioned to dispense the liquidto a location on a polishing surface outside the retaining ring.
 2. Theassembly of claim 1, wherein the reservoir comprises a recess formed inan upper surface of the polishing liquid delivery ring.
 3. The assemblyof claim 2, wherein the recess is an annular recess surrounding thecarrier head.
 4. The assembly of claim 2, wherein a passage is formedthrough the polishing liquid delivery ring from the reservoir to theoutlet.
 5. The assembly of claim 4, wherein the passage is essentiallyvertical.
 6. The assembly of claim 4, wherein the passage is tilted. 7.The assembly of claim 6, wherein the passage is angled outwardly fromtop to bottom.
 8. The assembly of claim 1, wherein the outlet is locatedon a bottom surface of the retaining ring.
 9. The assembly of claim 1,wherein the polishing liquid delivery ring includes a plurality ofoutlets in fluid communication with the reservoir, each outletpositioned to dispense the liquid to an associated location on thepolishing surface outside the retaining ring.
 10. The assembly of claim1, wherein the retaining ring has a bottom surface with slurry deliverychannels.
 11. The assembly of claim 1, wherein the polishing liquiddelivery ring includes an inwardly extending flange positioned on a topsurface of the carrier head.
 12. The assembly of claim 1, wherein theflange is positioned on a top surface of the retaining ring.
 13. Theassembly of claim 12, wherein the flange is positioned between the topsurface of the retaining ring and a bottom surface of a housing of thecarrier head.
 14. The assembly of claim 1, wherein the polishing liquiddelivery ring is coupled to the carrier head by a bearing.
 15. Theassembly of claim 1, further comprising a supply tube having an outletpositioned at least intermittently over the polishing liquid deliveryring.
 16. The assembly of claim 15, further comprising a carrier headsupport to hold the carrier head and a pump supported on the carrierhead support to pump polishing liquid through the supply tube.
 17. Theassembly of claim 16, further comprising a polishing liquid supplyfluidly coupled to the pump and secured to the carrier head support. 18.The assembly of claim 16, wherein the pump is configured to dispense thepolishing slurry into the reservoir intermittently during polishing. 19.The assembly of claim 16, wherein the pump is configured to dispense thepolishing slurry into the reservoir continuously during polishing.
 20. Amethod for delivering a polishing liquid, comprising: delivering apolishing liquid into a reservoir of a polishing liquid delivery ringcoupled to a carrier head; and dispensing the polishing liquid from thereservoir through an outlet in fluid communication with the reservoir toa location on a polishing surface outside a retaining ring of thecarrier head.